. 2013 Jul 4;178(6):890–897. doi: 10.1093/aje/kwt073

Table 3.

Risk of Basal-Cell Carcinoma According to Quintile of Cumulative UV-B Flux Exposure in Age- and Multivariate-adjusted Analyses, Nurses' Health Study (1986–2006) and Health Professionals' Follow-up Study (1988–2006)

Quintile of UV-B Flux Exposure	Median Value (Robertson-Berger Count × 10⁴)^a	No. of Cases	Person- Years	Age-adjusted		Multivariate-adjusted^b
Quintile of UV-B Flux Exposure	Median Value (Robertson-Berger Count × 10⁴)^a	No. of Cases	Person- Years	RR	95% CI	RR	95% CI
Nurses' Health Study
1	164	2,292	347,649	1.00	Referent	1.00	Referent
2	360	2,501	333,887	1.65	1.47, 1.84	1.63	1.45, 1.82
3	600	2,806	332,183	2.23	1.93, 2.58	2.19	1.89, 2.53
4	843	3,675	339,472	2.92	2.48, 3.43	2.84	2.41, 3.33
5	1,130	4,395	316,500	3.29	2.79, 3.88	3.18	2.70, 3.76
P_trend				<0.0001		<0.0001
Health Professionals' Follow-Up Study
1	154	1,107	131,104	1.00	Referent	1.00	Referent
2	350	1,286	131,938	1.30	1.13, 1.49	1.28	1.12, 1.47
3	565	1,721	132,572	1.68	1.42, 1.98	1.63	1.38, 1.93
4	791	1,960	126,775	1.91	1.60, 2.29	1.85	1.54, 2.21
5	1,080	2,163	128,548	1.99	1.65, 2.40	1.90	1.57, 2.29
P_trend				<0.0001		<0.0001
Pooled Analysis
1		3,399	478,753	1.00	Referent	1.00	Referent
2		3,787	465,825	1.47	1.16, 1.85	1.45	1.15, 1.83
3		4,527	464,755	1.94	1.47, 2.57	1.90	1.42, 2.53
4		5,635	466,247	2.37	1.56, 3.58	2.29	1.51, 3.49
5		6,558	445,048	2.56	1.56, 4.19	2.46	1.48, 4.09
P_trend				<0.0001		<0.0001
P for heterogeneity^c				0.004		0.002

Abbreviations: CI, confidence interval; RR, relative risk; UV-B, ultraviolet B.

^a Median cumulative midrange UV-B flux exposure for each quintile.

^b Multivariate analysis controlled for age, family history of melanoma, natural hair color, number of moles on an extremity, susceptibility to sunburn as a child/adolescent, lifetime number of severe/blistering sunburns, and cumulative UV-B flux exposure.

^c P value from a test of heterogeneity between studies.